The present invention relates to a method for controlling refrigerant pressure in an ambient heat exchanger of a refrigerant circuit, in particular in a heat pump circuit of a vehicle.
In the case of hybrid and electric vehicles, refrigerant circuits operable as a heat pump are increasingly considered for heating and/or air-conditioning or for cooling the passenger compartment or individual components of the vehicle. Refrigerant circuits operated as a heat pump absorb heat from the ambient air by an ambient-air heat exchanger. Under certain operating conditions, there is the risk of icing of the ambient-air heat exchanger, which would lead to a failure or to a significant reduction of the heating power of the heat pump circuit.
It is an object of the invention to control a refrigerant circuit in such a manner that icing of the ambient heat exchanger is prevented.
The starting point of the invention is the recognition that the danger of icing of the ambient heat exchanger will exist only when
a) the current dew point temperature of the ambient air is below 0° C., and
b) the temperature of the ambient heat exchanger or the vaporization temperature in the ambient heat exchanger is below the current dew point temperature.
The dew point temperature of the ambient air is a function of the ambient air temperature and of the humidity of the ambient air, which may be indicated as the relative air moisture φ or as absolute humidity x.
The basic idea of the invention consists of determining or estimating the current dew point temperature of the ambient air by measuring or determining the temperature of the ambient air and by measuring or by determining the humidity of the ambient air.